1. Field of the Invention
The present invention relates to making electrical contact between an electrically conductive carrier plate and an electrode of an electrical component, with the aid of and through an insulating adhesive.
2. Description of the Prior Art
Frequently, certain electrical components are made with a sheet of metal which is stamped into shape and serves as a carrier for an electrical element and which is securely connected to the electrical element to form a unit. For the most part, the two parts are connected together using a two-component adhesive or a fusion adhesive.
When such a carrier plate is connected, for example to a disc-shaped piezoceramic element such as is required for the oscillator disc of a timepiece or for the piezo transducer of a telephone, one refers to such structure as a sandwich plate.
In the case of the timepiece oscillator disc, as is well known in the art, the piezoceramic element has electrodes on both sides covering respective surfaces. The electrodes can be made of baked-on silver or metal coatings applied by vapor deposition. With this structure, one encounters the problem that the electrode on the adhesive side cannot be brought into contact with the carrier plate in a straightforward fashion. It is known for the carrier plate itself to be made of conductive material and for the two parts to be connected together using an adhesive of sufficiently low viscosity. Here, the difficulty arises through the fact that a sufficiently high contact pressure must be applied in order to form a satisfactory conductive connection between the carrier plate and the adhesive-side electrode. In order to ensure that, first of all, this contact pressure is not of necessity too high, and secondly, a good contact is established, an adhesive must be used which is sufficiently fluid when setting. In addition, the surface of the carrier plate must receive prior mechanical treatment in the form of roughening and/or extra scoring. This process is relatively expensive and cannot be easily automated. An adhesive suitable for this method takes 12 hours to set at 130.degree. C. and is therefore not economical for mass production.
When the sandwich plate is used in a piezo transducer for a telephone, the sandwich plate must be mounted delicately so that the oscillations of the piezoceramic element are not influenced. For this reason, in such an application contact cannot be made with a compression spring, as is possible with the timepiece oscillator disc, so that thin small connecting wires or strips, which do not influence the oscillations, must be soldered to the electrodes. To make this possible, it is already known from German Pat. No. 2,138,563, that the adhesive-side electrode must be extended around the component onto the other side of the ceramic disc. In order to pass the electrode about the disc, the ceramic disc must be orientated during screen printing and positioned in relation to the screen configuration. This is not without problems due to the fragility of the piezoceramic element and the required accuracy of screen printing the conductor.